An apparatus of this type, in which the inlet in the casing surface of the paperboard tube opens into the sample chamber, is known from DE-PS 30 00 201. A sampling device is there described in which the sample chamber has a lateral inlet for molten metals. The inlet opening terminates at the casing surface of the paperboard tube surrounding the sample chamber and is encased with a covering which forms a delayed-action device and closes off the inlet opening during the immersion process of the sampling device into the molten metal, so that when penetrating the slag layer an intrusion of contaminating particles into the chamber is prevented. The delayed-action device is destroyed after penetrating the slag layer and the inlet opening becomes accessible. The intrusion of slag during penetration through the slag layer is of course prevented by such a closure, but intrusion cannot be prevented through the then opened inlet of other types of contamination, as for example, gas bubbles or particles from the side covering intrude into the chamber and contaminate the sample.